This invention relates to color picture tubes having tension masks, and more particularly to a tension mask assembly having support members for connecting the tension mask to a frame.
A cathode ray tube (CRT) includes an electron gun for generating and directing three electron beams to the screen of the CRT. The screen is located on the inner surface of a faceplate panel of the CRT and is made up of an array of elements of three different color emitting phosphors. A color selection electrode, which may be either a shadow mask or a focus mask, is interposed between the gun and the screen to permit each electron beam to strike only the phosphor elements associated with that beam.
Recently, the CRT having a flatter faceplate panel has become more desirable. As the CRT becomes flatter, so does the need for flatter shadow masks. Such flat shadow masks tend to be prone to vibration, or microphonics, during tube operation, which adversely affects the display screen of the CRT. In order to reduce microphonics, the shadow mask is stretched and welded to support members. The support members are secured to a frame and assist in maintaining tension on the shadow mask. These types of mask that are stretched are commonly referred to as tension-type shadow masks.
The mask frames and support members used to support the tension shadow masks maybe advantageously constructed of sheet metal structures welded together to provide means for supporting the tension mask. The fabrication of such structures is often labor extensive and a relatively costly operation as a result of the many welds needed to strengthen the support members. The welding operation also subjects the support members to thermal expansions that may distort the support members affecting the placement of the mask with respect to the screen. Furthermore, during CRT manufacture, the tension mask-frame assembly is exposed to temperatures reaching or exceeding approximately 460xc2x0 C. At temperatures of this magnitude, the weld joints are subject to the potential of fatigue crack initiation at high stress points.
The present invention therefore provides an improved tension mask frame assembly in which mask support members are provided with side walls and a back wall that are held together without the need for welding.
Embodiments of the invention are provided in which the side walls and a back wall of the mask support member are attached to each other by a ridge on one side wall engaging the back wall. Alternatively, the back wall of the support member has tabs formed along an edge whereby each tab is received by a respective aperture preferably formed therethrough or is received between multiple ridges to secure the back to the sides producing a closed support member. In addition, the tabs are secured to the side walls, by engagement with the aperatures, such that any two adjacent walls are restricted from shifting resulting in a mask support member that is torsionally stiff.